1. Field of the Invention
This invention relates to an endoscope provided with an optical lens at the distal end of an inserting portion.
2. Description of Related Art
Generally, an endoscope comprises an operating portion and an inserting portion, and a lens frame holding an optical lens such as an objective is provided at the distal end of the inserting portion.
Conventionally, the optical lens has been directly bonded to the lens frame, as disclosed in Laid-Open Japanese Utility Model Application, Publication No. 59-141305.
In recent years, electrohydraulic calculus crushing apparatus have been used with endoscopes to crush calculi formed in kidneys, urethrae, biliary tracts, etc. The electrohydraulic calculus crushing apparatus comprises a power source unit and a flexible probe having electrodes at its tip. The probe is inserted in a channel of an endoscope, and the tip of the probe is protruded to approach the aimed calculus while one observes through the endoscope. When electricity is discharged between the electrodes provided at its tip, shock waves are produced to crush the calculus.
In this case, however, the shock waves produced between the electrodes at the tip of the probe affect the distal end portion of the endoscope. In a conventional endoscope in which the optical lens is directly bonded to the lens frame, the shock waves are transmitted to the optical lens without being absorbed. Thus, if a plurality of optical lenses are fixed to the lens frame and spaced from each other for focus adjustment, the bonding of the front optical lens may be loosened by the pressure of the shock waves, and the front optical lens may clash against an inner optical lens so that the lenses may be cracked. Even if a single optical lens is bonded to the lens frame, the pressure of the shock waves will be concentrated on a surface to which the optical lens is bonded, and the optical lens may be cracked from that portion. Further, the bonding agent between the optical lens and the lens frame may come off owing to the shock waves, and water may enter the lens frame so that waterdrops may remain on the lens or the water may also reach an optical fiber bundle located on the inner side of the optical lens to affect the optical fibers.